Pencil lead and the method of making the same



Patented Jan. 28, 1941 UNITED STATES PENCIL LEAD AND THE METHOD OF MAKING THE SAME Leonard E. Best, Summit, N. J.

Original application December 28, 1939, Serial No.

Divided and this application February 26, 1940, Serial No. 320,840

3 Claims.

This invention relates to pencil leads, and to the method of making the same and is a divisional application of application Serial No. 311,323 filed December 28, 1939.

The invention relates to the manufacture of lead pencils, and has special reference to the preparation of leads and crayons intended to be used when sheathed in a wooden casing and held therein by glue, or other water soluble adhesive.

In the manufacture of black leads (so-called). it is customary to impregnate the clay graphite mixes with waxes after baking. The waxy surface of these leads is water repellant, and in consequence the glue usually used in uniting the two sheaths of the wooden casing enclosing the leads, while it adheres to the wooden sheaths of the casing, does not join with the lead, whereby a looseness of the core of the pencil in respect to its sheathing casing results.

In contradistinction to these black leads which are made with graphite and clay and afterwards impregnated with wax, colored leads or crayons usually do not contain graphite but contain a considerable amount of wax. The same difiiculty above noted in connection with the graphite leads -in uniting two sheaths to bond the lead core to the casing is also presented in connection with these colored leads.

Many various attempts have been proposed to overcome the difliculty, and to increase the structural strength of the pencil point by treating the lead in such a manner that an adhesion of the lead core with the sheaths of the wooden casing is broughrt about to such an extent as to bond the lead and sheaths together.

One of these methods is the sulphuric acid dip to destroy the waxy surface. Another is to use chemical crystals between the core and the grooves of the casing; another is to subject the core of lead before it has been placed into the casing to a mechanical action, one of such mechemical means being the sand blast process.

The objections to these various methods of the prior art are that they are essentially dirty, dangerous to the operatives and relatively expensive, and as regards those that utilize the mechanical processes of indentation by sand blasting, for instance, while the peripheral surface of the leads are subjected to indentations, the wax which permeates the entire clay graphite mixture is merely compressed at such peripheral surface, and therefore is still present when the glue is being applied. While some of these attempts overcome certain objections, they present others. This invention overcomes many objections of the prior art, and it is simple, clean and inexpensive in operation; and the invention consists generally in the treatment of leads, either such as are known as black leads made of the clay graphite wax mixture. or the colored leads made of pigment and wax, to an electrical arcing action along the entire peripheral surface of the leads.

As the black leads contain graphite which is a conductor, the lead is used as a part of the electric circuit and subjected to an arcing action. whereas since the colored leads made of pigment and wax are non-conductors, they are not used as conductors but are subjected to the action of an electrical are which acts upon the peripheral surface of the lead to remove the outer peripheral surface insofar as the wax film is concerned, in the same manner as in the case of the are upon the black lead used as a conductor. The wax film being secured, in consequence, the clay graphite constituents on the one hand. and the pigment constituent on the other, come into direct contact with the glue in the sheaths of the casing and thereby an intimate adhesion between lead and casing is obtained, as a result of which the lead core, be it black lead or colored lead, is securely held in the wooden casing, and by such a secure holding the lead pencil at its point is structurally strengthened.

The invention will be further described in regards to the embodiments thereof, which will be shown in the drawing, and the invention will be finally pointed out in the claims.

In the accompanying drawing:

Figure l is a plan view of the improved machine which is utilized for the treatment of pencil leads made of clay, graphite and wax;

Figure 2 is a side View thereof;

Figure 3 is a drawing taken from a microphotograph of the outer surface of the lead after it has been treated in the machine shown in Figures 1 and 2;

Figure 4 is a transverse section taken on line 5-4 of Figure 3;

Figure 5 is an enlarged transverse section of the lead while it is being moved in the machine shown in Figures 1 and 2;

Figure 6 is a transverse section of the lead as imbedded in the two sheaths forming the casing; and

Figure 7 is a drawing of two electrodes with the colored lead therebetween whereby the colored lead is subjected to the arcing action of the electrodes.

Similar characters of reference indicate the same parts throughout the various views.

Referring to the drawing, and more particularly to Figure 6, there is there shown a finished lead pencil made up of the sheath in and the sheath II, each having a semicircular bore 12 which is provided with glue. Within these two semicircular bores 12 there is placed, after the glue has been applied thereto, a lead 13 which forms its core. The glue is also applied between the peripheral surfaces of the sheaths I and H, as at 14, and joins these together This is known.

The invention is shown as embodied in an enlarged view of the core l3 as shown in Figure 4, and this shows that the outer peripheral surface is irregular and partly pitted and partly otherwise removed by attrition, as shown by the various cavities relatively large or small indicated by IS in Figure 4. These indentations result from the removal of the wax film or coating of the lead. The removal of the wax somewhat inside of the initial periphery, is brought about by rotating a lead as shown in Figure 5, while moving the same, and subjecting it to an electric arc. In Figure 5 the general direction of the movement of the lead 13 is indicated by the arrow I6, and which movement is brought about by a pushing action of an upright rod l1 secured to a belt l8 moving in the direction of the arrow l9. Above the belt there are guide rods or tracks upon which the lead I3 rests. By the movement of the lead I3 in the direction of the arrow I 5, it is rotated in the direction of the arrow 2!, and as the lead I3 is part of an electrical circuit passing through the guide rail or tracks 20, an arcing action takes place as indicated by 22, as the circular outer surface of the load circumferentially leaves the guide rail 20. This arcing action acts upon the wax, and the high temperature of the arc probably volatilizes or decomposes the wax. and in consequence removes the same from the peripheral surface of the lead.

In Figure 5 the lead is shown in the position where about three-quarters of its circumference has already been acted upon and the remaining circumference, that indicated generally by 23, is relatively smooth, i. e., it has that smoothness usually attendant leads after they have been prepared and are generally ready for insertion in the casing.

In Figure 3 is shown a reproduction of a microphotograph showing the actions of the arcing upon the lead, described in connection with Figure 5.

The important thing, therefore, is to subject a lead consisting of a mix of clay, graphite and wax to an arcing action such as described in connection with Figure 5, as a result of which the exterior peripheral surface of the lead will have the wax portion removed so that the remainder of the composition such as the clay and graphite may readily bind with the glue when the pencil is being completed in commercial form, as described in connection with Figure 6. There is, of course, wax within the lead, and it is desirable to encase the arc-treated lead before the inner wax oozes to the free from wax surface.

One manner of treating the leads in accordance with the description of Figure 5 is shown in Figures 1 and 2. Inthe embodiment of the do vice or machine there shown, which may be varied so as to carry out the actions described in connection with Figure 5, there are in Figure 2 three standards 3! and 32, and adjabelt 31 is centrally disposed as shown in Figure 1,

and two belts 38, each narrower than the belt 31, are disposed in spaced relationship to each other. The belts are actuated by a pulley wheel 39 and belt 40, and by the operation of the pulley wheel 39, the shafts 35 are rotated due to the action of the belts.

Referring now to Figure 1, it will be seen that disposed at either side of the belt 31 there are tracks 20. and in the embodiment shown these tracks 20 converge from the standard 30 towards the standard 3|. These tracks 20 are each connected with an electrical conductor, one conductor being indicated by 4!, and the other by 42, and these conductors 4| and 42 are suitably connected with an electrical circuit operated by a switch 43, the electrical circuit having a transformer 44, the circuit being an alternating current circuit. Between the standards 3! and 32 the guide rails 20 also converge, and they converge towards the standard 32, and these guide rails or tracks 20 are continuous from the conductors 4| and 42, so that they are also under the action of the electrical current, the ends of the tracks 20 being insulated from each other by a suitable space or by a block of insulating material 45. A

As each of these tracks 20 are substantially one from the standard 30 to the standard 32, the arrangement of the belts 3'! and 38, as before described, is made, namely, in the wider space between the tracks 20, the belt 31 is between the tracks 20, whereas when these tracks converge to almost contact with each other, the belts 38 are spaced at each side thereof. Another reason for this arrangement is that it is desirous of subjecting the entire peripheral surface of each lead, as it moves from one end to the other of the machine, to the arcing action described. The belts themselves are provided with upright standing rods I1, and these rods are arranged in pairs, each pair acting upon a lead.

The operation of the machine described is as follows: The leads, and in this case the black leads made of a clay graphite mixed with wax, are inserted into the hopper 33, and they automatically drop upon the belt 31. As they drop upon this belt 31, a pair of upright rods I1 abut against each lead, and due to the movement of the belt in the direction of the arrow 41 the leads are moved in the direction of the arrow 41 and roll upon the tracks 20 at each side of the belt 31. It will be noted that the lead now indicated by l3a has its two ends within the tracks 20, so that the electrical arcing action takes place upon the lead from end to end inwardly. As the belt 37 moves the lead 13a to the position of the lead l3b, the arcing action works towards the center until the position of the lead reaches about that of He.

Thereafter, the lead is moved by the two belts 38, and the electrically actuated tracks 20 act upon the inner portion of the lead l3) as shown in Figure 1 until when the lead l3g reaches the position shown in Figure 1, the central portion of the lead has been arced, and thereby the arcing action has taken place throughout the entire length of the lead, and due to the rotation of the lead, has taken place throughout the circumference thereof. v V

In connection with the arcing action upon crayons or colored leads, the lead is subjected to a rotation action as shown by the arrow 5| in Figure 7 by roller means, and is moved longitudinally by suitable means through a gap 52 between the electrode 53 and the electrode 54. By the action of the arc between the electrodes 53 and 54, the peripheral surface of the colored lead I. is thereby acted upon in substantially the same' manner as described in connection with the leads I! in Figure l.

It has been seen that in treating black leads, the conductivity of the graphite is utilized to carry an electric current through the lead and by rolling the leads over a suitable set of tracks which form a part of the same electrical circuit that thereby a continuous series of small electrical surface discharges that destroy the waxy surface are obtained, whereby the leads so treated may be properly glued in the wooden sheaths, which form the casing. It has also been seen that in treating crayons which are non-conductors, the crayon is subjected to a continuous electrical discharge or electrical arc that completely surrounds it and carbonizes the surface waxes.

In both of these methods, relatively low voltages and current densities are used, so that they are essentially inexpensive and simple. The degree of treatment is readily controlled by the usual electrical instruments giving a wide range of effects at the will of the operator. The action of the process of treating the leads is rapid, and the necessary equipment so compact and inexpensive that it can form a very flexible addition to the existing processes for pencil manufacturing, and can be included in such a way that the processed leads can conveniently be used directly after processing before any deterioration takes place. It will be remembered that the wax permeates the entire lead, and it is therefore preferable to encase these leads within a reasonable time after their electrical treatment, to prevent the wax from the interior of the leads from oozing out to the surface.

When pencils are made using leads processed in the manner described and bonded to the sheaths, they are structurally strong and give greater service than those made with the conventional untreated leads.

The manifold indentations of. various configurations relatively large and small and varied in regards to contour serve as an excellent interstitial surface for the entrance of the glue, and bring about a binding'effect between the lead core and the casing.

It is believed that the wax which is acted upon by the electric arc or arcing action is either volatilized or carbonized, the carbonization due to the high temperature of the are being probably of the character of coking. It is now generally said that carbonization takes place up to 350 F. or 400 F., and coking about 500 F., and high temperature coking between 1000 F. and 1200 F. Graphitizing of carbon takes place beyond 1200 F., and generally around 1800 F. to 2300 F. or 2500 F. Wax used for impregnating leads melts at aboutv F. or F. and volatilizes or decomposes at about 400 F., these temperatures depending upon the particular constituency of the wax.

Various changesmay be made in the structural features of the machines described, the invention here being also the treatment by an electrical arc action upon the peripheral surface of a waxed lead, be it graphite or colored, whereby the peripheral surface is brought into a condition to obtain a permanent binding effect with the enclosing casing, and various changes may be made within the principle of the invention described without departing from the scope of the subjoined claims.

I claim:

1. Apparatus for treating pencil leads and the like, comprising a pair of stationary electrode members spaced from one another and producing an electric arc, means for feeding leads transversely across said electrode members, said electrode members converging toward one .another from said feeding means, and means for rolling said leads from said feeding. means along said electrode members, whereby saidleadsv are subjected throughout their entire length to saldelectric arc, to remove wax constituents from the outer periphery of said leads.

2. Apparatus for treating pencil leads and the like, comprising a pair of stationary horizontally extending electrode members spaced from one another and producing an electric arc, means for feeding leads transversely across said members, said electrode members converging toward one another from said feeding means, endless conveyor means disposed below said electrode members, and a series of longitudinally spaced members on said conveyor means adapted to engage respective leads fed from said feeding means for rolling the same along said electrode members, whereby said leads are subjected throughout their entire length to said electric arc to remove wax constituents from the outer periphery of said leads.

3. Apparatus for treating leads comprising a pair of spaced stationary supports converging toward one another, means for feeding leads onto said spaced supports, longitudinally movable means for rolling said leads along said supports, and electrical arc-making means connected with said spaced supports, whereby said leads are subjected to an electrical contact at different lengths thereof during their travel along said supports, to remove wax constituents from the outer periphery of said leads.

LEONARD E. BEST. 

